R. J. HARVEY-GIBSON AND M. KNIGHT—REPORT ON THE ALG. 403 
RHODOPHYCEA. 
32. SpPYRIDIA FILAMENTOSA, J. Ag. (With cystocarpia and antheridia.) 
*33, GELIDIUM CRINALE, Thur. 
*34. Liagora viscipa, Ag. (With cystocarpia and antheridia.) 
*35. DIGENEA SIMPLEX, Ag. 
*36. GALAXAURA ADRIATICA, Zan. 
Hauck (‘ Die Meeresaleen Deutschlands und Cisterreichs’) states that 
antheridia and tetragonidangia (tetrasporangia) are unknown in the genus. 
Only one plant of this species was present in the collection, but it was of 
special interest inasmuch that it bore both cystocarpia and tetragonidia. The 
gonidangia are developed on the terminal branches, and on surface view appear 
at the base of shallow depressions in the thallus. The main body of the thallus 
consists of loosely woven hyphee passing over into shorter cells lying at right- 
angles to the surface. The exterior ends of these cells abut on a subepidermal 
layer of large cells, covered in turn by a compact external layer of rather 
smaller cells, which present a mosaic on surface view. The superficial cells 
Surface view of the tetragonidial region. Tetragonidial region in section. 
x 450, x 450. 
are strongly calcified. The tetragonidia are formed in the subepidermal layer, 
and the mother-cell contents divide in the tetrahedral manner into the four 
tetragonidia. As the gonidangia mature the superficial cell-layer disappears, 
forming the shallow depression seen on surface view (figs. 1,2). Cystocarpia 
are formed in the same branch and at the bottom of similar depressions. 
While investigating the Marine Algz of the Isle of Man, we have 
been struck with the frequency with which we have met with sexual and 
asexual organs, not merely on the same plant but on the same branch. 
This phenomenon we have observed in Lophothalia byssoides, Calli- 
thamnion Hookeri, Callithamnion tetragonum, Callithamnion corymbosum, and 
B25 
